Twog
Twog is a simple application that parses an RSS feed and will tweet any posts it hasn't already tweeted. Once you obtain OAuth access to a twitter account and provide it in the configuration and run Twog, it will tweet a prefix, your blog title, and a URL of the post. There are also options of using Bit.ly for URL shortening and you can install Twog as a cron job for automated polling.
$ gem install twog